(1) Field of the Invention
The present invention relates to processing narrowband signal components, and more specifically to an efficient method for achieving a variable processing interval with a fixed Fast Fourier Transform (FFT) size and filter bandwidth.
(2) Description of the Prior Art
The FFT is an integral component of modern, digital signal processing because of the efficiency it provides in computing the Discrete Fourier Transform (DFT) of a given signal. Although FFT algorithms vary, the fundamental component of all FFT processing is the signal decomposition into successively smaller DFTs. These smaller DFTs exploit the cosine and sine function symmetry and periodicity to reduce the overall multiplications and additions, thereby allowing a transformation, i.e. a DFT, using relatively few computations.
Narrowband signals are characterized by a large power spectrum component, i.e., a peak as compared to the surrounding spectrum that occupies a narrow frequency window. Narrowband signals represent periodic or near-periodic time-domain signals. Because periodic signals typically occur over large time periods when compared to processing intervals, it is difficult to determine the correct processing interval to allow narrowband detection in the frequency domain. Processing intervals are further limited by computational constraints including processor speed, memory, filter design, and FFT size.
Conventional automated techniques exist for tracking narrowband signals using frequency domain features, while another approach allows narrowband tracking by time-domain signal processing. The existing automated tracking techniques are designed for processing limitations including filter bandwidth and sampling size; however, narrowband signal information is utilized beyond tracking purposes. There is currently not an efficient method for generating general narrowband signal information that effectively varies the processing interval while meeting system constraints including filter bandwidth and FFT size. What is needed is a system that generates narrowband information while effectively varying the processing interval, without imposing additional requirements on processor speed, FFT size, filter bandwidth and memory.